If your game crashes while it's framerates are low, the most likely cause is that the game can't handle the slow performance it is receiving from your PC. The solution thus is to make the game less demanding on your PC.

This step may be implemented by either reducing your graphic quality settings or downloading a mod or tool which reduces the quality of something. Even if you don't plan on reducing quality, it might be useful to download some of the performance enhancing mods which don't affect visual quality significantly so that you can crank up some of your graphics settings further.